Synucleinopathies are a group of clinically important, progressive neurological illnesses for which there are no approved therapies that can slow, halt or reverse progression. These diseases are defined by the presence of abnormal aggregates of the protein ?-synuclein within neurites and cell bodies, known as Lewy pathology. Lewy inclusions are found in brain regions where cell death occurs, but it is not clear how they relate to disease. Recent preliminary data in mouse models using sophisticated, new in vivo imaging approaches suggests that Lewy pathology forms out of the neuron's endogenous ?-synuclein after seeding with recombinant produced ?-synuclein fibrils. Furthermore, only neurons that develop Lewy inclusions are fated to die in these models. Critical questions remain, however, including whether human Lewy pathology is formed by similar mechanisms and if human neurons also die by similar pathways as those in fibril-seeded mouse models. In order to answer these questions, advanced electron microscopic (EM) approaches will be used. The long-term goal is to determine how Lewy inclusion-bearing cells degenerate in human disease in order to guide the development of therapies to halt this process. This proposal will test the central hypothesis that specific structural and molecular properties of Lewy inclusions drive associated neuronal cell death in fibril- seeded mouse models and humans with Parkinsonism. This will be tested in three specific aims: 1) Determine the Lewy inclusion structural & molecular characteristics that predict cell death. 2) Determine the mode of programmed cell death in Lewy inclusion-bearing neurons. 3) Test whether alteration of Lewy inclusion properties underlies aggressive forms of neurodegeneration. The proposed study will be conducted at Oregon Health & Science University in collaboration with consultants at the Mayo Clinic and the University of Pennsylvania, each with complementary expertise in EM approaches to study brain disease and the neuropathology of Parkinsonism. This K02 - Independent Scientist Award will provide the candidate with the expertise in advanced EM approaches needed to study this relationship of Lewy pathology to neurodegeneration. It will also involve a variety of structured coursework, workshops and formal advising programs in order to provide an excellent foundation for launching an independent research career. Ultimately, the knowledge gained has the potential to lead to new therapeutic strategies that target cell death in ways that treat Parkinson's disease, Dementia with Lewy Bodies and related disorders.